HIV-infected patients 21 years of age and older with chronic hepatitis C infection and a viral load greater than 2000 copies/mL may be eligible for this 2 1/2-year study. Candidates will be screened with blood and urine tests and possibly a liver biopsy, if a recent one is not available. The liver biopsy is done to determine the severity of liver disease. For this test, patients are admitted to the NIH Clinical Center for 1 to 2 days. A sedative is injected into an arm vein, the skin in the area over the biopsy site is numbed with a local anesthetic, and a needle is inserted rapidly into and out of the liver to obtain a small tissue sample. The patient remains in the hospital overnight for monitoring. A chest X-ray, electrocardiogram (EKG) and liver ultrasound are also done. Within 4 weeks of the screening tests, candidates who appear eligible for the study will have a physical examination, medical history and repeat blood tests. Women who can become pregnant will have serial pregnancy tests throughout the study.